The present invention relates to a prestress-monitoring element for screw-type anchors.
More particularly, it relates to a prestress-monitoring element which is arranged on an anchoring rod of a screw-type anchor between an article to be fixed to a wall or the like and a screw element of the screw-type anchor.
In screw connections it is always of great importance that the prestress required for reliable fixing is produced by a sufficiently powerful tightening of a screw. Too great a prestress may possibly lead to fracture during mounting, but on the other hand too low a prestress can lead to problems in function and problems of reliability. As a rule, with screw-type mountings it is not the prestress but the tightening torque by means of a torque wrench that is monitored. This has the disadvantage, however, that the torque allows no direct conclusion as to the prestress force, since different parameters exert great influence on the degree of conversion between torque and prestress force. Thus, for example, a greased or co-rotating washer has just as serious effect on the prestress as a dirty washer. With the same tightening torque, it is quite possible for fluctuations in the prestress force of .+-.50% to occur.
A further problem arises in that in practice the use of torque wrenches is frequently neglected, even though monitoring of the tightening torque is prescribed. This leads to the known disadvantages. In addition, it is not possible to check the conventional screw-type anchors and other types of screw connections subsequently for the presence of the required prestress force in the particular screw connection.